As is known, light-emitting devices, such as light emitting diodes (LEDs), based upon porous silicon are of great interest on account of their possible integration in semiconductor circuits manufactured with standard processes of a complementary metal oxide semiconductor (CMOS) type. However, the luminous efficacy of LED devices based upon porous silicon may be poor.
LED devices of a known type, for example, described by G. Barillaro et al., in “Integrated porous-silicon light-emitting diodes: A fabrication process using graded doping profiles”, Applied Physics Letters, Vol. 78, No. 26, Jun. 25, 2001, include a substrate of a P-type housing a porous-silicon region, which extends from the top face of the substrate for a depth of some microns.
Extending into the porous-silicon region are one or more cathode contacts of an N+ type, which have a depth less than the maximum depth reached by the porous-silicon region.
During use, by applying a difference of potential between the N+ contacts and the back of the substrate, a current flows through the porous-silicon region, generating emission of photons, in a per se known manner. However, the portions of the porous-silicon region that extend underneath the N+ contacts do not take part in the emission of photons towards the outside of the device on account of the masking caused by the N+ contacts.
Other embodiments describe formation of porous silicon only at the sides of the N+ contacts and not also underneath them. However, in this case, the current flows mostly at the interface between the N+ contacts and the substrate, which has an electrical resistance lower than the resistance of the interface between the N+ contacts and the porous silicon. Thus, in either case the luminous efficacy of the LED device may not be satisfactory. This effect may give rise to an unsatisfactory luminous efficacy.